Device for treatment of molten cast iron in vessels

ABSTRACT

Magnesium is conveyed from a feeder by compressed gas into molten cast iron at the rate of 2 - 4.5 g/s-t through a tuyere with an evaporator, immersed into molten cast iron. The tuyere is made in the form of a metal pipe with a flaring-out nozzle which is provided with side holes, serves as an evaporator and is covered with refractory lining, the relation of the tuyere evaporator inside diameter in the section passing through the upper edge of the side holes to the evaporator height from the upper edge of the side holes to the point where the tuyere pipe opens into the evaporator being from 0.3 to 0.8.

United States Patent Voronova et a1.

[451 Apr. 29, 1975 Filed: Aug. 24, 1973 Appl. No.: 391,252

US. Cl. 266/34 T; 75/130 BB Int. Cl. C2lc 7/00 Field of Search 75/130 A, 130 AB, 130 B,

75/130 BB. 130 C; 266/41, 34 A, 34 T Z Y 2' U [56] References Cited UNITED STATES PATENTS 1,019,965 3/1912 Kelly 266/34 T 2.525973 10/1950 Sundstrom et a1. 266/34 T 2.803.533 8/1957 Bicniosek et a] 266/34 T 3.080.228 3/1963 Hale et a1. 75/130 BB 3,231,371 l/l966 Schaeffcr et a1 75/130 BB FOREIGN PATENTS OR APPLICATIONS 226.108 1/1969 U.S.S.R. 266/34 T Primary E,\'uminerGerald Av Dost Attorney, Agent, or Firm-H01man & Stern 1 1 ABSTRACT Magnesium is conveyed from a feeder by compressed gas into molten cast iron at the rate of 2 4.5 g/s-t through a tuyere with an evaporator. immersed into molten cast iron. The tuyere is made in the form of a metal pipe with a flaring-out nozzle which is provided with side holes, serves as an evaporator and is covered with refractory lining, the relation of the tuyere evaporator inside diameter in the section passing through the upper edge of the side holes to the evaporator height from the upper edge of the side holes to the point where the tuyere pipe opens into the evaporator being from 0.3 to 0.8.

1 Claim, 3 Drawing Figures DEVICE FOR TREATMENT OF MOLTEN CAST IRON IN VESSELS The present invention relates to a device for the treatment of molten cast iron and more specifically it relates to desulphurization, refining and inoculation of molten cast iron.

Known in the previous art is a method of treatment of molten cast iron with magnesium in vessels wherein powdered magnesium is introduced in a stream of carrier gas into molten metal through a tuyere with an evaporator.

Industrial experiments with this method have shown that its efficiency, particularly while treating cast iron in big vessels depends on the intensity of magnesium supply into molten cast iron (in g/s-t) and on the concentration of magnesium in the carrier gas (in kg/m At a low-intensity injection of magnesium into molten cast iron, particularly in big vessels, the object of treatment (desulphurization, refining and inoculation of cast iron) is not achieved and the degree of magnesium assimilation by the molten metal proves to be low since such a procedure fails to ensure sufficient mixing of the entire amount of metal in the vessel and its continuous renewal in the zone of reactions which occur in the cast iron when the latter is being treated with magnesium.

At a highly intensive supply of magnesium into molten cast iron, violet evaporation of magnesium causes the cast iron to splash out of the vessel, which is undesirable; besides, a considerable proportion of magnesium vapours leaves the molten metal without having a chance of reacting with its components.

When compressed air is used for carrier gas, the efficiency of the method of treating cast iron by injected powdered magnesium depends also on the concentration of magnesium in compressed air.

A low concentration of magnesium in the air leads to heavy losses of magnesium due to its oxidation by the oxygen contained in the air.

An excessively high concentration of magnesium impairs its pneumatic conveyance through tubes so that the delivery of magnesium into molten cast iron is of a pulsating, nonuniform nature.

The nonuniformity of magnesium delivery into cast iron causes it to splash out of the vessel and clogging of the tuyere pipe at the point where it opens into the evaporator.

An object of the invention lies in providing a device for treatment of molten cast iron in vessels wherein the entire amount of cast iron in the vessel would be mixed intensively with magnesium vapours.

Another object of the invention lies in providing a device for treatment of molten cast iron with magnesium vapours in which the cast iron would not be splashed out of the vessel and which would ensure a high degree of magnesium assimilation by the cast iron.

These and other objects are accomplished by provid ing a device for treatment of molten cast iron in vessels wherein powdered magnesium is injected in a stream of carrier gas into molten metal through a tuyere with an evaporator. According to the invention the rate of magnesium delivery is from 2 to 4.5 g/s-t.

It is practicable that the concentration of magnesium in the carrier gas should be from 5 to kg/m.

Known in the art is a device for the realization of the method comprising a feeder which supplies magnesium for the treatment of cast iron, a tuyere in the form of a pipe with a flaring-out nozzle which functions as an evaporator and has side holes for the escape of the magnesium vapours into molten cast iron, pipelines interconnecting the evaporator and tuyere with the source of compressed carrier gas which conveys magnesium into molten cast iron.

The use of this device renders it possible to disperse the magnesium vapours leaving the evaporator throughout the volume of the cast iron being treated which calms down the process of treatment (reducing the splashing out of metal from the vessel) and raises the degree of magnesium assimlation by the molten metal.

Besides, the gas cushion formed in the evaporator by the vapours of magnesium and carrier gas protects the outlet opening of tuyere pipe against contact with the molten metal which reduces the danger of this opening being clogged in the course of treatment.

However, the experience gained in operating this known device has demonstrated that its operational reliability (complete elimination of clogging where the tuyere pipe opens into the evaporator) depends on the relation between the inside diameter of the evaporator at the section passing through the upper edge of the side holes and the height of the evaporator from the upper edge of the holes to the point where the tuyere pipe opens into the evaporator.

If this relation is large, clogging of the tuyere pipe at the outlet into the evaporator is not eliminated so that the device is not perfectly reliable.

If this relation is small, the evaporator space becomes rapidly covered with splashes of metal, slag and the products formed by interaction of magnesium with the molten metal (MgO, MgS, etc.) so that the danger of clogging at the point where the tuyere pipe enters the evaporator is not eliminated either.

An object of the invention resides in eliminating the aforesaid disadvantages.

For the realization of the method we hereby provide a device comprising a magnesium feeder, a tuyere in the form ofa pipe with a flaring-out nozzle which functions as an evaporator and has side holes for the escape of magnesium vapours into molten cast iron, pipelines interconnecting the feeder and the tuyere with a source of compressed carrier gas which conveys magnesium into molten cast iron. According to the invention, the relation of the inside diameter of the tuyere evaporator in the section passing through the upper edges of the side holes to the evaporator height from the edge of the side holes to the point where the tuyere pipe opens into the evaporator is from 0.3 to 0.8.

The use of the device according to the invention wherein said relation (0.3 0.8) of the evaporator height from the upper edge of its side holes to the point where the tuyere pipe opens into the evaporator to its diameter in the section passing through the upper edge of said side holes of the evaporator ensures reliable and efficient assimilation by the cast iron of magnesium injected into it at the rate of 2 to 4.5 g/s-t.

This occurs owing to the fact that at the above-stated relation of the evaporator height to its diameter the surface of molten metal is located at such a distance from the point where the tuyere pipe opens into the evaporator which rules out the clogging of the pipe with splashes of molten metal. On the other hand, the diameter of the evaporator ensures a sifficiently large volume of the latter, i.e., the volume of the space where magnesium is evaporated and where it vapours are accumulated in a quantity ensuring their uniform delivery into the molten metal through the side holes of the evaporator, without pulsations and bursts.

It is expedient that the relation of the tuyere evaporator inside diameter in the section passing through the upper edge of the side holes to the inside dimeter of the tuyere pipe should be from 10 to 25.

Now the invention will described in detail by way of example with reference to the accompanying drawings:

FIG. 1 is a schematic diagram of the device for the realization of the method of treatment of molten cast iron in vessels according to the invention:

FIGS. 2 and 3 are other designs of the evaporator in the tuyere of the device according to the invention.

The device for the realization of the method of treatment of molten cast iron comprises a feeder 1 (FIG. 1) in the form of a metal pressure vessel from which magnesium is delivered into cast iron; a tuyere 2 in the form of a hollow metal pipe 4 (FIGS. 2 and 3) provided on the outside with refractory lining 3, having a flaring-out nozzle 5 (FIG. 2) and 5a (FIG. 3) with side holes 6 (FIG. 2) or 7 (FIG. 3) said nozzle functioning as an evaporator; said tuyere is inserted into molten cast iron 9 contained in a ladle 8 for the time of magnesium injection the relation of the inside diameter D of the evaporator 5 or 50 at the section passing through the upper edge of the side holes 6 or 7 to the height H of the evaporator 5 or 5a from the upper edge of the side holes 6 or 7 to the point where the pipe 4 opens into the evaporator 5 or 5a being from 0.3 to 0.8; pipelines I0. 11 and 12 with a pipeline 10 connected to the source of compressed carrier gas and intended to supply gas into the pipelines l1 and 12, the pipeline 11 being connected to the evaporator l for filling it with the carrier gas required for conveying magnesium into the pipeline 12, while the pipeline 12 is connected directly to the tuyere 2 and is intended for delivering magnesium together with the carrier gas into the tuyere, the section of the pipeline 11 adjoining the feeder 1 and the section of the pipeline 12 adjoining the tuyere 2 being made of a flexible hose; a batchmeter 13 installed in the lower part of the feeder 1 and intended to ensure an accurately metered supply of magnesium from the feeder 1 into the pipeline 12 (the batchmeter may be of a cell, screw or air type, or of any other type capable of changing the rate of magnesium supply into the molten cast iron in the process of its treatment).

A valve 14 is intended to cut off the entire device from the source of carrier gas; a valve 15 cuts off the feeder 1 from the source of carrier gas on completion of treatment, when loading magnesium into the feeder, etc., and controls the gas pressure in the feeder in the course of operation; a valve 16 cuts off the tuyere 2 from the source of carrier gas on completion of treatment and after withdrawing the tuyere 2 from metal 9; a valve 17 is intended for letting out the gas from the evaporator on completion of cast iron treatment and while loading magnesium into the feeder 1.

Pressure regulators l8 and 19 maintain the preset pressure of carrier gas in the pipelines 11 and 12 in the course of operation.

A flowmeter 23 mounted on the pipeline l0 measures the consumption of carrier gas required for the treatment of cast iron.

A dynamometer 24 from which the feeder 1 is suspended, shows the amount of magnesium delivered into the cast iron being treated.

The carrier gas can be either compressed air, nitrogen, or any other inert gas, e.g. argon.

The carrier gas can be drawn from an industrial compressed air system of from such individual sources as compressors, bottles, etc.

It is preferable to install the device for the realization of the method of treatment of cast iron in vessels by injecting powdered magnesium in a stream of a carrier gas, according to the invention, on a special trestle under which the cast iron is treated, and to locate the trestle on the route by which the cast iron is conveyed from the point of melting to the point of its utilization, e.g. between the blast-furnace plant and the steel foundry or between the blast furnace plant and the pigcasting machine.

The device operates as follows.

Molten cast iron is poured into the ladle 8 which is then carried to the point where the cast iron is treated with magnesium.

The feeder 1 is loaded through pipe 25 (FIG. 1) with powdered magnesium by any conventional method (by pouring, by pneumatic conveyance, etc.).

The carrier gas is delivered from the source (not shown) through the pipelines l0 and 11 into the feeder 1 while the pipeline l2 delivers the carrier gas into the tuyere 2. Meanwhile, the valves 14, 15 and 16 are open and the valve 17 is closed.

As soon as the pressure of the carrier gas reaches the preset limit in the feeder l and the tuyere is also filled with carrier gas, the tuyere 2 is immersed into the vessel 8 with molten cast iron 9 sufficiently deep to ensure that the open end of the evaporator is quite close to the vessel bottom. At this moment the pressure of gas in the feeder l which depends on how deep the tuyere has been immersed into molten cast iron should be somewhat higher that the ferrostatic pressure of molten metal at the tuyere immersion depth.

After immersing the tuyere 2 into molten cast iron to the preset depth the batchmeter l3 admits magnesium from the feeder 1 into the pipeline 12 where the particles of magnesium are entrained by the stream of the carrier gas and delivered in the form of a gaspowder mixture through the pipe 4 of the tuyere 2 on to the surface of molten cast iron located in the lower part of space A of the evaporator 5 or 5a (FIGS. 2, 3). On entering the evaporator 5 or 50, the magnesium melts and evaporates, its vapours are injected together with the carrier gas through the evaporator side holes 6 (FIG. 2) or 7 (FIG. 3) into the cast iron being treated where they interact with the components of the molten metal (sulphur, oxygen).

Bubbles of magnesium and carrier gas vapours rising to the surface of the cast iron mix the latter which is conducive to better assimilation by the cast iron of magnesium and to cleaning of the molten metal of gases, nonmetallic inclusions and graphite.

Depending on whether the process of cast iron treatment proceeds quietly or violently, the rate of magnesium delivery can be changed by the batchmeter 13. If the process is sluggish (poor mixing of cast iron in the vessel) the magnesium delivery should be increased 5 and conversely, if the process 'of treatment is too violent, with metal splashing out of the vessel, the delivery of magnesium is decreased until splashing ceases.

The preset pressure in the feeder l in the course of treatment can be maintained by the valve 15.

After the required amount of magnesiumhas been injected into the cast iron, its delivery from the feeder 1 into the pipeline 12 is discontinued and the tuyereis withdrawn from the metal.

After withdrawing the tuyere 2 from the cast iron, the supply of carrier gas into the pipelines 11 and 12 is cut off by means of valves l5, 16 or 14 and the gas remaining under pressure in the feeder is discharged into the atmosphere through the pipe 26 with the aid of the valve 17. This completes the process of treatment of cast iron.

The duration of treatment of cast iron with magnesium depends on the amount of metal in the vessel, the required quantity of magnesium per 1 ton of cast iron and the rate of magnesium delivery into the molten cast iron.

Given below are examples of treating molten foundry iron in the device according to the present invention.

The cast iron has been treated with granulated magnesium injected into the metal in a stream of compressed air, the treatment being preformed directly in molten cast iron transfer ladles which carry the cast iron from the blast furnace to the point of treatment.

Magnesium has been introduced into the cast iron through a tuyere with an evaporator in which the relation ofits inside diameter in the section passing through the upper edge of the holes to its height from the upper edge of the holes to the point where the tuyere pipe opens into the evaporator has been 0.5.

EXAMPLE 1 Cast iron has been treated with a view to achieve deep desulphurization (to a sulphur content not over 0.005 percent) and produce high-quality pig iron. The initial sulphur content in pigs before treatment has been 0.045 percent; oxygen content 0.011 percent. Amount of cast iron in the ladle, 96-t (the rated capacity of the ladle being 120 t).

The cast iron has been treated under the conditions stipulated in the present invention: rate of magnesium delivery into cast iron 2.5 g/s-t, concentration of magnesium in air 6.0 kg/m.

The consumption of magnesium per 1 t of cast iron has been 0.7 kg and the duration of treatment, 4.6 min.

After desulphurization the cast iron has been poured into pigs on a pig-casting machine.

The obtained results are as follows:

Final sulphur content in cast iron 0.004%; Final oxygen content 0.00371; Degree of desulphurization of cast iron 91%; Degree of magnesium assimilation for desulphurization and deoxidation of cast iron 617r EXAMPLE 2 Cast iron has been treated under the conditions other than stipulated in the invention: rate of magnesium delivery into cast iron 1.2 g/s-t, concentration of magnesium in air 4.0 kg/m.

The rated capacity of the ladle and the weight of metal in the ladle have been the same as in Example 1.

Final sulphur content in cast iron after treatment 0.020% Final oxygen content 0.00671 Degree of desulphurization 55% Degree of magnesium assimilation for desulphurization and deoxidation of cast iron 38% EXAMPLE 3 Cast iron has been treated with a view to its inoculation and producing castings (ingot moulds) with spheroidal graphite.

The initial sulphur content in cast iron before treatment has been 0.040 percent, oxygen content 0.010 percent, amount of cast iron in the ladle 60 t (rated ladle capacity t).

The cast iron has been treated in accordance with the conditions stipulated in the invention: rate of magnesium delivery into cast iron has been 40 g/s-t, concentration of magnesium in the air delivered into the cast iron, 17.0 kg/m.

The consumption of maagnesium has been 1.70 kg per 1 t of cast iron, the duration of treatment being 8.5 min.

After inoculation, the ladle with cast iron has been transferred into the iron foundry for casting ingot moulds.

The following results have been obtained:

Final sulphur content in cast iron after It can be seen from the above examples (No. 1 and 3) that the injection of magnesium into molten cast iron through a tuyere with an evaporator according to the invention and the observance of the treatment conditons as stipulated in the invention (rate of magnesium delivery into cast iron from 2.5 to 4.0 g/s-t and concentration of magnesium in the air fed into the cast iron 6 17 kg/m", the consumption of magnesium being 0.7 kg per 1 t of cast iron) have ensured deep desulphurization of cast iron with a final sulphur content of 0.004 percent and the degree of magnesium assimilation exceeding 60 percent.

Under the same conditions but with a consumption of 1.70 kg of magnesium per 1 tof cast iron it has been possible to produce a high residual content of magnesium in metal required for obtaining spheroidal graphite in the castings (the residual magnesium content in cast iron in Example 3 is 0.05 percent).

Example 2 proves that non-observance of the treatment conditions according to the invention impairs the results obtained, viz., deep desulphurization is not achieved and the degree of magnesium assimilation is sharply reduced.

The method according to the invention renders it possible to treat large amounts of molten foundry iron with magnesium in metal lurgical industry since said method fits easily into the production process of metallurgical plants, is highly efficient and controllable, and is distinguished for simplicity and productivity.

We claim:

1. A device for treatment of molten cast iron with magnesium in vessels, comprising: a feeder in the form of a pressure vessel which supplies magnesium for the treatment of cast iron; a tuyere in the form of a pipe connected with said feeder. having a flaring-out nozzle at one end acting like an evaporator and provided with side holes, said end of the tuyere with the evaporator being immersed into the molten cast iron for the supply of magnesium; the relation of the inside diameter of said evaporator in the section passing through the upper edge of the side holes to the height of said evaporator from the upper edge of said side holes to the point where the hole of the tuyere pipe opens into the evaporator is from 0.3 to 0.8; a pipeline connecting said tuyere with a source of compressed gas and with said evaporator; a pipeline connecting said feeder with a source of compressed gas whose pressure delivers magnesium from the feeder into said pipeline which connects said tuyere with the source of compressed gas, the magnesium being entrained by compressed air flowing through this pipeline towards said tuyere, carried through said pipe and tuyere evaporator wherefrom it is injected in a vapourized state through said evaporator holes into molten cast iron thus treating the latter. 

1. A device for treatment of molten cast iron with magnesium in vessels, comprising: a feeder in the form of a pressure vessel which supplies magnesium for the treatment of cast iron; a tuyere in the form of a pipe connected with said feeder, having a flaring-out nozzle at one end acting like an evaporator and provided with side holes, said end of the tuyere with the evaporator being immersed into the molten cast iron for the supply of magnesium; the relation of the inside diameter of said evaporator in the section passing through the upper edge of the side holes to the height of said evaporator from the upper edge of said side holes to the point where the hole of the tuyere pipe opens into the evaporator is from 0.3 to 0.8; a pipeline connecting said tuyere with a source of compressed gas and with said evaporator; a pipeline connecting said feeder with a source of compressed gas whose pressure delivers magnesium from the feeder into said pipeline which connects said tuyere with the source of compressed gas, the magnesium being entrained by compressed air flowing through this pipeline towards said tuyere, carried through said pipe and tuyere evaporator wherefrom it is injected in a vapourized state through said evaporator holes into molten cast iron thus treating the latter. 